Transformer having ventilating passages



Dec. 15, 1970 R. L. SCHWAB TRANSFORMER HAVING VENTILATING PASSAGES FiledJfine 24; 1969 3 Sheets-Sheet 1 PRIOR ART INVENTOR RlChGl'd L Schwob FATTORNEY as I PRIOR ART FIG IA k '4 Q 70 l WITNESSES Dec. 15, 1970 R. L.SCHWAB 3,548,354

TRANSFORMER HAVING VENTILATING PASS AGES Filed June 24, 1969 3Sheets-Sheet 2 liq I94 FIG.2.

, FIGS.

Dec. 15, 1970 R, SCHWAB 3,548,354

TRANSFORMER HAVING VENTILATING PASSAGES Filed June 24, 1969 3Sheets-Sheet 3 &

United States Patent O 3,548,354 TRANSFORMER HAVING VENTILATING PASSAGESRichard L. Schwab, Sharon, Pa., assignor to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed June24, 1969, Ser. No. 836,065 Int. Cl. H01f 27/10 US. Cl. 336-57 9 ClaimsABSTRACT OF THE DISCLOSURE An electrical transformer of the fluid cooledtype, having a winding which includes a plurality of pancake coilsdisposed about a vertically oriented winding leg of a magnetic core,with the pancake coils being spaced to provide horizontal coil ducts,and with a vertical duct located adjacent the openings in the pancakecoils, which communicates with the coil ducts. A manifold is providedabout the outer edges of the pancake coils, which is formed of inner andouter spaced tubular insulating members. The inner tubular insulatingmember has a plurality of openings disposed therein which are alignedwith the coil ducts.

BACKGROUND OF THE INVENTION (1) Field of the invention The inventionrelates in general to electrical transformers, and more specifically toelectrical power transformers of the concentric coil, core-form type.

(2) Description of the prior art In the application of forced oilcooling to electrical power transformers of the concentric coil,core-form type, wherein the high voltage winding includes a plurality ofpancake coils spaced to provide coil ducts, the prior art modifies thecoils by placing duct formers between the coil turns when winding thecoils, or utilizes a plurality of bafiles to direct the oil flow in azig-zag manner across the major surfaces of the pancake coils.

The former arrangement increases the manufacturing cost of the winding,adversely aflects the coil space factor, and weakens the windingstructure mechanically. The latter arrangement substantially increasesthe cost of the winding due to the labor involved in inserting thebaflling arrangement required to provide the desired flow path.

Therefore, it would be desirable to be able to construct the pancakecoils for transformers which are to be forced oil cooled, in the samemanner as the pancake coils which are cooled by thermal siphon flow.Further, it would be desirable to be able to assemble the pancake coilsinto a winding assembly for forced oil cooled transformers, withoutrequiring the additional labor of disposing a plurality of discretebaflles adjacent inner and outer edges of predetermined pancake coils.

SUMMARY OF THE INVENTION Briefly, the present invention is a new andimproved fluid cooled power transformer of the concentric coil,core-form type, having a magnetic core-winding assembly disposed in atank and immersed in an insulating and cooling fluid, such as oil. Themagnetic core-winding assembly includes a winding having a plurality ofpancake coils disposed in spaced relation with one another about avertically oriented leg of the magnetic core. The spaced coils providehorizontally disposed coil ducts which communicate with a vertical ductlocated adjacent the inner openings of the coils. Inner and outerconcentrically disposed, spaced insulating tubular structures encirclethe winding assembly, with the inner tubular structure having aplurality of openings therein aligned with the coil ducts, and with thetwo tubular structures cooperating to provide a manifold for thedistribution of fluid to the coil ducts. Pumping means forces the fluidto flow from a plenum chamber at the bottom of the transformer tank intothe manifold, through the coil ducts, to the vertical duct adjacent theedges of the coil openings.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of theinvention will become more apparent when considered in view of thefollowing detailed description and drawings, in which:

FIGS. 1 and 1A are fragmentary, elevational views, in section, oftypical winding arrangements of the prior art for forced oil cooledtransformers;

FIG. 2 is a fragmentary, elevational view, in section, of a windingarrangement for forced oil cooled transformers constructed according tothe teachings of an embodiment of the invention;

FIG. 3 is a fragmentary elevational view, in section, of a windingarrangement for a forced oil cooled transformer, constructed accordingto another embodiment of the invention; and

FIG. 4 is a perspective view, partially cut away, of a three-phasetransformer constructed according to the embodiment of the inventionshown in FIG. 3

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, andFIG. 1 in particular, there is shown a fragmentary elevational view, insection, of a high voltage winding 10 for a transformer of the core-formtype. FIG. 1 illustrates a prior art arrangement for forced oil coolingthe high voltage winding, which requires a modification of the coils ofwhich the winding is formed.

Specifically, FIG. 1 illustrates a plurality of pancake type coils 12,14, 16 and 18, shown on only one side of a centerline 20, since they aresymmetrical, with the pancake coils being disposed with their majorsurfaces in a horizontal plane, and spaced from one another to providecoil ducts between their horizontal major surfaces. Baflies in the formof cylindrical insulating tubular members 22 and 24 are disposedadjacent the inner and outer edges of the pancake coils to direct theforced flow of the cooling fluid, such as oil, through the coils. Thepancake coils are wound with duct formers therein such as corrugatedstrips of pressboard, which separate the turns of the pancake coilswhile providing ducts therein for the flow of the cooling fluid. Forexample, pancake coil 12 is illustrated with ducts 26, 28 and 30, andthe remaining pancake coils have similar cooling ducts. The flow ofcoolant, illustrated by the arrows, under the urging influence of apump, flows around the coils, through the horizontal coil ducts, andthrough the ducts disposed through the coil turns, to remove the heatgenerated in the windings. While this arrangement is functionallysuitable, it has the disadvantage of requiring that the pancake coils bemodified from the form in which they are used in transformers cooled bythe natural thermal siphon effect, which increases the manufacturingtime and cost of the coils and winding. Further, the duct formersincrease the radial build dimension of each coil, which increases theyoke dimension of the magnetic core resulting in the utilization of morecore material, it increases the length of the magnetic circuit, and itadversely affects the space factor of the winding.

FIG. 1A illustrates another prior art engagement for cooling the highvoltage winding of a power transformer of the core-form type, which doesnot require that the pancake coils be modified. Specifically, FIG. 1A isa fragmentary elevational view, in section, of a high voltage windingwhich includes a plurality of pancake coils 42, 44, 46, 48 and 50, whichare symmetrical about centerline 52, and spaced axially apart to providea plurality of coil ducts between the major surfaces of the pancakecoils, such as coil ducts 54, 56, 58 and 60. Insulating bafile members62 and 64- are disposed adjacent the inner and outer edges of thepancake coils to direct the flow of cooling fluid to the coils, and acomplex arrangement of baffles is used to direct the flow of coolingfluid in a zig-zag configuration across the major surfaces of thepancake coils. For example, a batfle 66 is disposed to block the duct atthe inner edge of coil 50, a bafile 68 is disposed to block the duct atthe outer edge of pancake coil 48, a baflie 70 blocks the duct at theinner edge of pancake coil 46, a baflie 72 blocks the duct at the outeredge of pancake coil 44, and a baffle 74 blocks the duct at the inneredge of pancake coil 42. The cooling fluid, indicated by the arrows,under the urging influence of a pump, is forced to flow around the outeredge of pancake coil 50, inwardly through coil duct 60, outwardlythrough coil duct 58, inwardly through coil duct 56, and outwardlythrough coil duct 54-. This arrangement is functionally suitable, buthas the disadvantage of the time required to construct the intricatebaffling system, with a typical winding phase requiring placing andsecuring in the order of 10 to 12 insulating washer shaped membersadjacent the inner and outer edges of the pancake coils of the winding,in order to achieve the desired zig-zag cooling arrangement.

FIG. 2 is a fragmentary elevational view, in section, of a phase of atransformer of the core-form type, constructed according to a firstembodiment of the invention, which provides eflicient cooling of thewindings without modification of the pancake coils, and withoutrequiring an intricate baffling arrangement. Specifically, phaseassembly 80 includes high and low voltage windings 82 and 84,respectively, disposed about a vertically oriented leg 86 of a magneticcore, with the windings 82 and 84 and leg 86 being symmetrical aboutvertical centerline 88. Low voltage winding 84 includes a plurality ofconductor turns, indicated generally at 90, which are insulated from themagnetic core leg 86 by insulating means 92. The high voltage winding 82includes a plurality of pancake coils, such as pancake coils 94, 96, 98,100, 102, 104, 106, 108, 110, 112, 114 and 116, each having a pluralityof radially superposed conductor turns such as turns 118 in pancake coil116. The pancake coils, such as pancake coil 94, have first and secondmajor opposed outer surfaces 120 and 122, joined by an opening 124 whichextends between these outer surfaces. The pancake coils are all disposedon a vertically oriented winding leg 86 of the magnetic core with theiropenings in alignment, and they are axially spaced to provide horizontalcoil ducts between their major surfaces, such as coil ducts 126, 128,130, 132, 134, 136, 138, 140, 142, 144 and 146.

Means, such as circumferentially spaced insulating members space theedges of the coil openings from the high-low insulation 142 between thehigh and low voltage windings 82 and 84, to provide a vertical coolingduct 150, which communicates with the plurality of horizontally disposedcoil ducts between the major surfaces of the pancake coils. The verticalduct is blocked at its lower end, in this embodiment, with suitableinsulating means 152, such as an insulating washer member, while theupper end of this duct is open.

Then, instead of a solid external wrapper or tubular baflie about theouter periphery of high voltage winding 82, as is common in prior artcooling arrangements, an external insulating wrapper or tubular barriermember 154 is provided which has a plurality of openings therein, whichopenings are aligned with the horizontal coil ducts between the pancakecoils. More specifically, barrier 154 has a plurality of axially spacedrows of openings, with each row having a plurality of circumferentiallyspaced openings adjacent one of the horizontal coil ducts. Further, aswill be hereinafter explained, the circumferential length of theopenings changes from row to row, in order to effectively equalize thelength of the parallel cooling paths, resulting in a highly eflicientand uniform cooling of the phase assembly 80. FIG. 2 illustrates one ofthe openings of each of the axially spaced rows of openings with theseopenings being given the reference numerals 160, 162, 164, 166, 168,170, 172, 174, 176, 178 and 180. Barriers 182 and 184, such as washershaped insulating members, are disposed between barrier 154 and thelower and upper pancake coils 116 and 94, respectively, to direct thecooling fluid to the horizontal coil ducts through the openings inbarrier 154.

The next step in creating the new and improved cooling system for phaseassembly 80, is to create a manifold about the high voltage winding 82,from which cooling fluid may enter the openings in barrier 184. Themanifold is created by an outer wrap or tubular insulating barriermember which is disposed about and spaced from the barrier 154. Suitablevertically oriented spacers may be attached to the outer periphery ofbarrier 154, or to the inner surface of barrier 190-, at predeterminedselected circumferential increments, to provide the desired spacebetween the two barriers, and define a space or manifold 192 between thebarriers which is blocked at its upper end by blocking means 194, andopen at its lower end. Thus, as illustrated by the arrows in the figure,the cooling fluid under the urging influence of a pump, is directed bysuitable baffles into the lower end of manifold 192. From manifold 192the fluid flows into the plurality of openings in each of the axiallyspaced rows of openings, to flow in the horizontal coil ducts to thevertical duct 150. The fluid then flows upwardly through vertical duct150, and is ejected from the winding assembly 80 at the upper end ofthis duct.

The embodiment of the invention shown in FIG. 2 has many advantages overprior art cooling arrangements. The pancake coils do not requiremodification. Ducts between the turns of the coil are'not required. Thepancake coils for the forced cooled transformer may thus be made in thesame way as the pancake coils for transformers which are cooled by thenatural thermal siphon effect. Further, an intricate bafl lingarrangement is not required. The only insulating washer members requiredare disposed at the extreme ends of the winding structure. Thus, verylittle additional labor is required to construct the phase windingassembly 80. The embodiment of the invention shown in FIG. 2 also hasthe advantage of introducing fluid into each coil duct at substantiallythe same temperature, as the fluid enters each horizontal coil duct froma manifold which draws the fluid from the cool fluid in a plenum chambernear the bottom of the transformer tank. The fluid is not required toproceed from coil duct to coil duct, picking up heat and temperature asit goes, as the fluid is directed through only one coil duct and thendischarge from the winding structure. Thus, the cooling of the windingis more eificient and uniform than prior art methods.

If it is desirable to direct the cooling fluid through two coil ductsbefore being discharged from the winding assembly, the manifold may beaxially divided into first and second vertically spaced sections, withthe fluid being directed from the first section of the manifold throughthe communicating horizontal coil ducts, and into the inner vertical.ducts, and then from the inner vertical duct into the remaining coilducts which communicate with the vertical duct, and then into the secondsection of the manifold. This embodiment of the invention is shown inFIG. 3, with like reference numerals in FIGS. 2 and 3 indicating likecomponents.

The phase winding assembly shown in FIG. 3 is given the referencenumeral 80, in order to indicate that it is a modification of the phasewinding assembly 80 shown in FIG. 2. Winding phase 80 of FIG. 2 may bemodified to provide winding phase 80', by removing the blocking means194 from the upper end of manifold 192, by disposing blocking means,such as an insulating washer member 200 between insulating barriers 154and 190 at substantially the mid-point of the axial length of highvoltage winding 82, to provide first and second axially spaced sectionsin manifold 192, referenced 210 and 212, respectively, by disposingblocking means 202 between the outer periphery of the pancake coillocated at the midpoint of winding 82, such as pancake coil 106, and theinner wall of barrier 154, and by blocking the upper end of verticalduct 150 with means 204, such as an insulating washer member.

In the modified phase winding structure 80, the cooling fluid enters thebottom of the first section 210 of manifold 192, and enters thehorizontal coil ducts 146', 144, 142, 140 and 138, through openings 160,162, 164, 166 and 168, respectively. The fluid flows inwardly throughthese openings in their associated horizontal coil ducts until reachingthe vertical duct 150, and flows upwardly therein and into thehorizontal coil ducts 136, 134, 132, 130, 128 and 126. The fluid flowsoutwardly in these coil ducts to the second section 212 of manifold 192,and then upwardly where the heated fluid is discharged from the phasewinding assembly 80'. This arrangement enables the cooling fluid toenter and leave the phase winding assembly 80' adjacent the outerperiphery at the ends of the structure, which in some instances may bepreferable to the embodiment of the in vention shown in FIG. 2 whereintheheated fluid exits the phase winding assembly 80 adjacent the inneredge of the high voltage winding.

FIG. 4 is a perspective view of a three-phase transformer 220 of thecore-form type, shown partially cut away in order to illustrate theteachings of the invention. Transformer 220 is constructed according tothe teachings of the invention shown in the embodiment of FIG. 3, andwill more fully illustrate the construction of the phase windingassemblies which equalizes the lengths of the oil flow paths, and thusimprove the cooling efficiency and the uniformity of the cooling, of thedisclosed arrangement.

More specifically, transformer 220 includes a magnetic core-windingassembly 222 disposed in a tank 224, with the tank 224 being filled to alevel 226 with an insulating and cooling fluid, such as mineral oil, orone of the synthetic cooling fluids, such as those containingchlorinated diphenyl and trichlorobenzene, with level 226 being selectedto completely immerse the magnetic core-winding assembly 222 in theinsulating and cooling fluid. The tank 224 has a plurality of openings228 disposed at level 226, which are connected to external coolers orheat exchangers (not shown), which are mechanically connected topredetermined outside walls of the tank 224. The cooled fluid from theheat exchangers is collected in suitable headers, and pumped back intothe tank 224 near the bottom thereof, such as via pump 230 throughopening 232 in the casing 224. The transformer 220 may have a pluralityof heat exchangers and pumps, as required by the specific application.

Magnetic core-winding assembly 222 includes a threephase magnetic core234, having winding legs 236, 238

and 240 connected at their ends by upper and lower yoke portions 242 and244, respectively.

Magnetic core 234 is formed of a plurality of stacked metalliclaminations, such as grain oriented silicon steel, with the winding legshaving a cruciform cross-sectional configuration in order to moreefficiently couple windings having round openings therein. The stackedlaminations are held in assembled relation by upper and lower end frameassemblies 246' and 248, respectively.

The magnetic core-winding assembly 222 also includes phase windingassemblies 250, 252 and 254, disposed about winding legs 236, 238 and240, respectively. Each of the phase winding assemblies includesconcentrically disposed low and high voltage windings, as shown moreclearly in FIGS. 2 and 3, and each of the high voltage windings have aplurality of axially spaced pancake coils. For example, phase windingassembly 250 includes high and low voltage windings 260 and 262,respectively, with high voltage winding 260 having a plurality ofpancake coils, such as pancake coils 264, 266 and 268, which are axiallyseparated by spacer members, such as spacer member 270, which spacersextend radially outward from the openings in the pancake coils to theouter periphery of the coils, and circumferentially spaced about themajor surfaces of the pancake coils. Spaces 270 may extend outwardlypast the outer periphery of the pancake coils, to space the first outerwrap or tubular barrier member from the edges of the pancaker coils, ifdesired. The plurality of pancake coils are mechanically held togetherat each end of the winding assembly by pressure rings or plates, such aspressure plate 272 shown at the bottom of phase winding assembly 250,and pressure plate 274 shown at the top of phase winding assembly 252.Suitable means, such as bolts 276 which are connected to the end frame,apply pressure to discrete points about the upper and lower pressureplates of each phase winding assembly, to provide the necessary force tohold the windings together and prevent them from distorting during shortcircuit stresses.

The three phase winding assemblies in FIG. 4- illustrate various stepsin the construction of a cooling system according to the teachings ofthe invention. For example, phase winding assembly 250 illustrates highvoltage winding 260 immediately after the pancake coils have beenassembled in spaced relation, phase winding assembly 252 illustrates thefirst wrap of insulation being applied to the winding assembly, andphase winding assembly 254 illustrates the second or outer wrap ofinsulation being applied to the winding assembly.

More specifically, the first step in constructing the cooling systemaccording to the teachings of the invention, illustrated relative tophase winding assembly 252, is to provide an insulating structure orbarrier member 280 which includes a rectangular sheet of insulatingmaterial precut to include a plurality of axially spaced rows ofopenings, with each row of openings including a plurality of spacedopenings, and with the sheet of insulating material being preassembledwith the spacer members er barrier member, which will be hereinafterdescribed.

More specifically, since this embodiment is similar to the embodiment ofthe invention shown in FIG. 3, wherein the manifold is axially dividedinto two spaced sections, two similar patterns of openings are provided,one for each section of the manifold. If the manifold has only onesection, like the embodiment of the invention shown in FIG. 2, therewould only be one basic pattern, which would extend completely acrossthe axial length of the winding assembly. Each row of openings includesopenings of a similar circumferential length, but the circumferentiallength of the openings in different rows of the pattern are different.Specifically, the circumferential length decreases from row to row asthe pattern extends vertically upward. Thus, as shown in FIG. 4, thefirst row of the first or bottom pattern includes a plurality ofcircumferentially spaced openings 282 each having a predetermineduniform circumferential length, and each aligned with the coil ductbetween the first two pancake coils at the bottom of the high voltagewinding. The next row of openings has the same number ofcircumferentially spaced openings as the first row, aligned with thenext coil duct, but the circumferential length of these openings, suchas opening 284, is less than the circumferential length of the openingsin the first row. This pattern of progressively shorter openings isrepeated across the first section of the manifold, and then the samepattern is repeated across the second section of the manifold. Theprogressively shorter openings equalize the effective length of the flowpaths from the manifold. Starting with the first section of themanifold, the longest flow path is from the bottom opening, while theshortest is from the top opening. Therefore, the circumferential lengthof the openings are progressively decreased from row to row as the firstsection of the manifold is progressed vertically upward, in order tomake the effective length of the fiow paths the same, to equalize thefluid flowing through the horizontal ducts, and to obtain uniform andefficient cooling. The same basic pattern is repeated in the secondsection of the manifold, as the manifold for the second section is theupper half of duct 150, and the longest flow path from this manifold isthrough the bottom row of openings associated with the upper manifoldsection.

The insulating barrier 280 may have spacer members attached to its outersurface, such as spacers 290 and 292. Two spacers, with a small gapbetween their adjacent ends, are required for the complete axial lengthof the structure, since a circumferential washer member 294 is disposedabout barrier 280 at its midpoint, which divides the manifold into thetwo axially spaced sections. A plurality of additional spacer members,such as spacer members 296 and 2%, are disposed at selected incrementsabout the circumference of the barrier, to adequately space the nextbarrier member from barrier member 280.

Next, a solid sheet of insulating material is wrapped about the innerbarrier member 280, to provide insulating barrier 300, which isillustrated relative to phase winding assembly 254. The outer wrap orbarrier member 300 is spaced from barrier 280 by the spacer members andwasher member, hereinbefore described, to define a manifold having firstand second axially spaced sections.

A horizontally disposed sheet-like member 301 is disposed to provide aplenum chamber at the bottom of the tank for the cooled fluid returningfrom the heat exchangers. Member 301 is disposed at a level whichcoincides with the bottom of the winding assemblies 250, 252 and 254,and has openings therein which are in communication with the bottomopenings to the manifolds defined by the spaced barrier members, such asbarrier members 280 and 300. Thus, the cooled fluid from the externalheat exchangers is directed into the plenum chamber at the bottom of thetank, and into the manifold associated with each phase winding assembly.The fluid flows into the lower section of the manifold, and then throughthe horizontal coil ducts to the inner vertical duct. The fluid thenenters the horizontal coil ducts which are in communication with theupper section of the manifold, it flows outwardly to the second sectionof the manifold, and then it leaves the winding assembly as illustratedby the arrows in FIG. 4, to flow to the outlets 228 connected to theexternal heat exchangers.

In summary, there has been disclosed a new and improved electricaltransformer which has a highly efficient structure for uniformly forcecooling the phase winding assemblies thereof, which has severaladvantages over arrangements of the prior art for accomplishing the samefunction. For example, the pancake coils of the high voltage windingassemblies may be constructed in the same manner as though thetransformer were to be cooled by the natural thermal siphon effect, andthe baffling system required is minimal and simple, thus adding verylittle to the manufacturing cost of the transformer. Further, the

cooling fluid is distributed to the horizontal coil duct via a manifold,which introduces fluid of substantially the same temperature to each ofthe ducts communicating with the manifold, and the openings in thebarrier associated with the manifold which communicate with thehorizontal coil ducts are arranged to equalize the flow paths throughthe various coil ducts, resulting in uniform cooling of the pancakecoils across the winding structure.

Since numerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. An electrical transformer comprising:

a tank,

an insulating and cooling fluid disposed in said tank,

a magnetic core-winding assembly disposed in said tank and immersed insaid fluid,

said magnetic core-winding assembly including a magnetic core having atleast one winding leg, and at least one winding which includes aplurality of pancake coils, each of which have first and second majoropposed surfaces and an opening which extends between the majorsurfaces, said at least one winding leg of the magnetic core beingdisposed through the openings in said plurality of pancake coils, withsaid winding leg being oriented and said pancake coils being spaced toprovide horizontal coil ducts between their adjacent major surfaces,

first means providing a vertical duct adjacent the edge of the inneropenings of said pancake coils, which communicates with the horizontalducts, second means disposed about the outer periphery of said pancakecoils having a plurality of axially spaced rows of circumferentiallyspaced openings therein, which communicate with the horizontal ducts,

third means disposed in spaced relation about said second means, saidsecond and third means defining a manifold filled with said fluid,

and means blocking the manifold to provide a fluid flow path whichincludes the manifold, the horizontal ducts, and vertical duct providedby said first means.

2. The electrical transformer of claim 1 including pump means whichforces the fluid to flow from the manifold, through the coil ducts, andupwardly through the duct provided by the first means.

3. The electrical transformer of claim 1 wherein the means blocking themanifold is at the upper end thereof, and including means blocking thevertical duct at the lower end thereof.

4. The electrical transformer of claim 1 wherein the means blocking themanifold divides the manifold into first and second axially spacedsections, and including means blocking the vertical duct at its upperend, providing a predetermined flow path for the fluid which includesthe first section of the manifold, the coil ducts which communicate withthe first section of the manifold, the vertical duct provided by thefirst means, the coil ducts which communicate with the second section ofthe manifold, and the second section of the manifold.

5. The electrical transformer of claim 4 wherein the circumferentiallengths of the openings in the second means progressively decrease fromrow to row across the first section of the manifold in a verticallyupward direction, with the pattern being repeated across the secondmanifold in the vertically upward direction.

6. The electrical transformer of claim 4 including pump means whichforces the fluid to flow in the predetermined flow path.

7. The electrical transformer of claim 1 wherein the circumferentiallengths of the openings in the second means in any predetermined row aresubstantiallv the same, but being of different circumferential lengthsin dif- References Cited ferent rows.

8. The electrical transformer of claim 7 wherein the UNITED STTESPATENTS different circumferential lengths of the openings in the1,703,410 2/1929 Smlfl} second means in different rows is predeterminedto r 3,028,566 4/ 1962 Cam1111 33660X equalize the effective lengths ofthe flow paths through THOMAS J. KOZMA, Primary Examiner US Cl. X.R.

the Winding.

9. The electrical transformer of claim 7 wherein the circumferentiallengths of the openings in the second 336 60 means progressivelydecrease from row to row across the 10 manifold in a vertically upwarddirection.

